The present invention relates to a method for determining the position coordinates of a target object and a device for determining the position coordinates of a target object.
A method and a device are known from EP 0 481 278 A1 for determining two- or three-dimensional position coordinates of a target object. The device comprises a laser distance measuring device, a camera device, a reference device and a control device. The laser distance measuring device has a transmitting element that transmits a laser beam and a receiver element that receives as a reception beam a laser beam at least partially reflected on the target object. The reference device has a first and second axis arranged perpendicular to each other and spanning an internal coordinate system; a third axis of the coordinate system is perpendicular to the first and second axes through the intersection of the axes. The device also includes a first and second angle measuring device for determining an azimuth angle and an elevation angle. The target object is sighted precisely through the camera device while the target axis of the laser distance measuring device and the sighting axis of the camera device are aligned to the target object. The laser distance measurement is performed by the laser distance measuring device and the angle values for the azimuth and elevation angles are determined by the angle measuring devices. The two-dimensional position coordinates are calculated from the distance value and the azimuth angle, the elevation angle is also necessary for the three-dimensional position coordinates.
The known device for determining the position coordinates of a target object has the disadvantage that at least one angle measuring device is necessary, which increases the complexity and cost of the device for determining the position coordinates. Furthermore, the laser beam must be precisely aligned to the target object for the laser distance measurement and the angle measurement.
The object of the present invention is to develop a method for determining the position coordinates of a target object in two or three dimensions that is suitable for interior use. In addition, a suitable device for the invention's method is to be developed for determining the position coordinates of a target object, where the position coordinates can be calculated with high accuracy with limited equipment expense.
This object is achieved according to the invention in the method for determining the position coordinates of a target object, and in the device for determining the position coordinates of a target object.
According to the invention, the method for determining the position coordinates of a target object in a measurement range in at least two dimensions has the following steps:                a target device with a reflector element is positioned on the target object,        a laser beam is transmitted by a transmitting element of a laser distance measuring device onto the target device,        at least a part of the laser beam is partially reflected on the reflector element,        an image of the target device with the at least partially reflected laser beam is recorded as light reflection by a camera device,        a focus of the light reflection is determined in the image of the target device,        the laser beam at least partially reflected on the reflector element is received as the received beam by a receiver element of the laser distance measuring device,        a distance to the target object is calculated from the received beam,        a first offset is calculated from a focal length of the camera device, the calculated distance to the target object, and a first image coordinate of the focus of the light reflection,        the position coordinates of the target object are calculated from the distance and the first offset.        
Determining the position coordinates of the target object with the help of a laser distance measurement and a light reflection in an image of a camera device has the advantage that no expensive angle measuring device is necessary, yet the position coordinates can be determined with a high accuracy. The reflector element of the target device produces a reflected laser beam that is visible in an image of the target device as light reflection. The invention's method is suitable for stationary targets and moving targets.
In a development of the method, a second offset is calculated from the focal length of the camera device, the distance to the target object, and a second image coordinate of the focus of the light reflection, and the position coordinates of the target object are additionally calculated from the second offset. The second offset enables determination of three-dimensional position coordinates of a target object in a measurement space. Among other things, the geometry of the target device determines whether the method for determining two- or three-dimensional position coordinates can be used. For determining two-dimensional position coordinates, a target device in the shape of a circular cylinder or a circular cylinder section is used, and for determining three-dimensional position coordinates a spherical or spherical-segment-shaped target device is used.
Preferably, a sequence of images of the target device is recorded with the camera device. The laser beam directed at the target device can be formed as an expanded laser beam with an aperture angle greater than 80°, as a moving laser beam, or as a moving laser beam with an aperture angle smaller than 10°. The expansion of the laser beam can occur in one direction or in two directions perpendicular to the propagation direction of the laser beam. With an expanded, non-moving laser beam, the laser beam is at least partially reflected on the reflector element of the target device and produces in the image of the target device a light reflection. If the camera device records a sequence of images of the target device, the light reflection is visible so long as the laser beam is transmitted. With a moving laser beam, the camera device records both images of the target device with light reflection and images without light reflection.
In a first variant of the method, from the sequence of the images recorded with the camera device the image with the strongest light reflection is determined as the image of the target device with the light reflection. The first variant is suited mainly for moving laser beams in which the sequence of the images recorded with the camera device has both images with light reflection and images without light reflection. The image with the strongest light reflection can be determined with the help of known image processing techniques.
In a second variant of the method, the image of the target device with the light reflection is determined by averaging over multiple images from the sequence of images recorded with the camera device. The second variant is suitable mainly for non-moving laser beams in which the light reflection in the images is visible so long as the laser beam is transmitted. The averaging over multiple images with a light reflection can be done with the help of known image processing techniques.
In a preferred embodiment of the method, the recording of the images of the target device with the camera device and the distance measurement to the target device with the laser distance measuring device are started simultaneously by a control device. The laser distance measuring device and the camera device are synchronized by the simultaneous start of the distance measurement and the recording of the images of the target device. The synchronization is advantageous for moving target objects. Since the measurement time for a distance measurement and the exposure time for the camera device usually differ from each other, the distance values and the images of the target device are not determined at the same time. The measured distance values and recorded images of the target device can be associated with each other through the synchronization. The closer to each other the times of the distance measurement and the recording of the image, the smaller the error in the position coordinates. For fast-moving target objects, the correct assignment between distance value and recorded image of the target device is important to limit the error.
Especially preferably, an image of the target device recorded by the camera device is associated by the control device with a distance value measured by the laser distance measuring device. The correct assignment between the measured distance values and the recorded images of the target device is mainly important for fast-moving target objects to reduce inaccuracies in the position coordinates. The control element of the laser distance measuring device can assign to each measured distance value a time after the start of the distance measurement, and the control element of the camera device can likewise assign to each recorded image of the target device a time after the start of the image recording. Through the simultaneous start, an evaluation element of the control device can assign the measured distance values and the recorded images of the target device to each other. An example of a suitable criterion for the assignment is that the image of the target device following in time is assigned to a distance value or the distance value following in time is assigned to an image.
For performing the invention's method in particular, the invention's device for determining the position coordinates of a target object in a measurement range in at least two dimensions comprises:                a target device with a reflector element that specifies the position coordinates of the target object,        a laser distance measuring device with a transmitting element that transmits a laser beam, a receiver element that receives as the received beam a laser beam at least partially reflected by the reflector element, and a control element,        a camera device with a receiver device and a control element,        a reference device with a first axis and a second axis, where the first and second axes are arranged perpendicular to each other and intersect at an intersection, and        a control device with a control element for controlling the laser distance measuring device and the camera device, and an evaluation element for calculating the position coordinates of the target object.        
The invention's device makes it possible to determine the position coordinates of a target object without an angle measuring device. The fact that an angle measuring device is not necessary makes it possible to realize an inexpensive device that can measure the position coordinates of the target object with high accuracy. The distance measurement with the laser distance measuring device and the recording of the target device's images with the camera device can be started at the same time through the control element of the control device.
In a preferred embodiment, the reflector element is designed as a rotationally symmetrical body or as a section of a rotationally symmetrical body. The geometry of the target device's reflector element decides whether the device can be used for determining two- or three-dimensional position coordinates. Circular cylinders or circular cylinder sections are suitable as a reflector element for two-dimensional measurements, and spheres or spherical sections are suitable for three-dimensional measurements. A rotationally symmetrical body has the advantage that the distance from the surface to the center is identical from all directions. The position coordinates of the target object lie on the cylinder axis of the circular cylinder or in the center of the sphere. The radius of the circular cylinder or the sphere is stored in the control device or entered into the control device by the operator. To calculate the position coordinates, the radius of the target device is added to the measured distance of the laser distance measuring device and to the image coordinates of the light reflection.
In a first variant, the laser distance measuring device has a beam shaping optical system that expands the laser beam with an aperture angle greater than 80°. The expansion of the laser beam can occur in one direction perpendicular to the propagation direction or in two directions perpendicular to the propagation direction of the laser beam. The expansion in one direction produces a line beam that is suitable for determination of two-dimensional position coordinates, and the expansion in two directions produces a spherical segment-like expanded laser beam for determination of three-dimensional position coordinates.
The expansion of the laser beam by a beam shaping optical system offers the possibility of using a stationary laser distance measuring device. The meter with the laser distance measuring device is disposed outside the measurement range or on the edge of the measurement range and arranged such that the expanded laser beam can cover the entire measurement range. The expansion of the laser beam with an aperture angle greater than 80° is mainly suited for determination of two-dimensional position coordinates. If the laser beam is expanded spherical-segment-like in two perpendicular directions each by an aperture angle greater than 80° and if the laser beam has limited power the danger exists that the power density for the received beam is too low for the evaluation. If there is sufficient power available in the laser beam, then a spherical-segment-like expanded laser beam with aperture angles greater than 80° can be used for determining three-dimensional position coordinates.
The term “beam shaping optical system” includes all beam shaping optical elements that expand, collimate, or focus a laser beam. The beam shaping optical system can consist of one optical element into which one or more optical functions are integrated or of multiple optical elements arranged one after the other. Cylinder lenses, cone mirrors, and similar optical elements are suitable as beam shaping optical systems for expanding a laser beam.
Particularly preferably, the beam shaping optical system expands the laser beam in a direction substantially parallel to the measuring plane. The beam shaping optical system particularly preferentially collimates or focuses the laser beam in a direction substantially perpendicular to the measuring plane. This beam shaping optical system is mainly suitable for determination of two-dimensional position coordinates and has the advantage that the laser beam's available power is used optimally. In determining two-dimensional position coordinates in the measuring plane, no expansion of the laser beams in the direction perpendicular to the measuring plane is necessary. The limited power of the laser beam is distributed in the measuring plane.
In a second variant, the laser distance measuring device has a motor unit, where the motor unit pivots the laser beam around an axis of rotation perpendicular to the measuring plane or around a pivot point. The rotation of the laser beams is useful if the power density of the laser beams after the expansion is too low to obtain a received beam strong enough for the laser distance measurement. The rotation of the laser beam around the axis of rotation perpendicular to the measuring plane can be performed as a rotating, scanning or tracking movement. In the rotating movement the laser beam is rotated continuously around the axis of rotation, in the scanning movement it is periodically moved back and forth around the axis of rotation, and in the tracking movement the laser beam follows the target device. The rotation of the laser beam around a pivot point is provided for the determination of three-dimensional position coordinates and is preferably used with a tracking device that follows the moving target device. The motor unit of the second variant can be combined with a beam shaping optical system that collimates or focuses the laser beam.
In a third variant, the laser distance measuring device has a beam shaping optical system and a motor unit, where the beam shaping optical system expands the laser beam with an aperture angle of up to 10° and the motor unit moves the laser beam around an axis of rotation perpendicular to the measuring plane or around a pivot point. The expansion of the laser beam and the rotation around an axis of rotation (two-dimensional) or a pivot point (three-dimensional) can be combined. The laser beam is expanded by a beam shaping optical system up to 10° and the expanded laser beam is moved by a motor unit around an axis of rotation or around a pivot point. The combination of beam expansion and rotation enables detection of a received beam with a power density strong enough for the evaluation of the light reflection. The expansion of the laser beam can occur in one or two directions perpendicular to the propagation direction of the laser beam. The rotation of the laser beam can be performed as rotating, scanning or tracking movement.
In a first preferred embodiment, the target device of the invention's device is attached to a hand-held tool apparatus. When work is being done with the hand-held tool apparatus, the tool apparatus's current position coordinates can be determined with the invention's device.
Exemplary embodiments of the invention are described below based on the drawings. These do not necessarily represent the exemplary embodiments to scale; instead, where useful for the explanation the drawing is produced in schematic and/or slightly distorted form. Reference is made to the relevant prior art with respect to additions to the teachings that can be directly learned from the drawing. It must be kept in mind that various modifications and changes to the form and detail of an embodiment can be made without deviating from the invention's general idea. The invention's features disclosed in the description, the drawings and the claims can be essential both individually by themselves and also in any combination for the invention's development. In addition, all combinations of at least two of the features disclosed in the description, drawings, and/or claims fall within the invention's framework. The invention's general idea is not restricted to the exact shape or detail of the preferred embodiment shown and described below or limited to a subject matter that would be restricted compared to the subject matter claimed in the claims. With the given dimensions, values lying within the stated limits should also be disclosed as limit values and ones that can be used and claimed at will. For the sake of simplicity, the same reference signs are used below for identical or similar parts or parts with identical or similar function.